tako-sdk-js

name	tako-sdk-js
description	tako.sh SDK: fetch handler interface, tako runtime object, generated tako.d.ts type augmentation, defineChannel/defineWorkflow, Vite and Next.js adapters.
type	framework
library	tako.sh
library_version	0.0.1
sources	["tako-sh/tako:sdk/javascript/src"]

Tako SDK (tako.sh)

Runtime SDK for JavaScript/TypeScript apps deployed with Tako.

CRITICAL: The tako.sh package is required — it provides the entrypoint binaries that tako-server launches to run your app. Tako v0 uses plain ES modules everywhere — no Tako global. Runtime state (env, secrets, logger, build info) is accessed through the tako object from tako.sh; channels and workflows are imported from their own files.

CRITICAL: Framework helpers are opt-in. Use tako.sh/vite for Vite-based SSR frameworks (TanStack Start, Nuxt, SolidStart) and tako.sh/nextjs for Next.js standalone builds. Plain fetch-handler apps do not need either helper.

Core Concept: The Fetch Handler

Tako apps export a standard fetch handler as the default export:

// src/index.ts — this is a complete Tako app, no SDK import needed
export default function fetch(request: Request, env: Record<string, string>) {
  return new Response("Hello World!");
}

The handler signature is:

type FetchHandler = (request: Request, env: Record<string, string>) => Response | Promise<Response>;

Two export forms are supported:

// Form 1: default export is the fetch function
export default function fetch(req: Request, env: Record<string, string>) {
  return new Response("OK");
}

// Form 2: default export is an object with a fetch method
export default {
  fetch(req: Request, env: Record<string, string>) {
    return new Response("OK");
  },
};

Package Exports

Import path	Purpose	Key exports
tako.sh	Isomorphic runtime + authoring helpers	tako, imageUrl, channels, workflows, storage URL option types, runtime types
tako.sh/server	Server-only runtime re-export	tako, TakoRuntime
tako.sh/client	Browser-safe channel client	Channel, configureChannels
tako.sh/react	React hook for channels	useChannel
tako.sh/vite	Vite plugin for SSR builds	tako() plugin function
tako.sh/nextjs	Next.js standalone adapter + wrapper	withTako(), createNextjsAdapter(), createNextjsFetchHandler()
tako.sh/runtime	Browser-safe runtime internals	loadSecrets, createLogger, Logger
tako.sh/internal	Server-only plumbing for framework-adapter boot	handleTakoEndpoint, initServerRuntime, channel/workflow helpers

Runtime state: tako.sh + tako.d.ts

tako generate emits a project-local tako.d.ts that augments tako.sh with typed environment names, typed tako.secrets keys, typed tako.storages names, channel metadata, workflow metadata, and runtime env globals. It keeps an existing declaration in app/, src/, or the project root; otherwise it uses an existing legacy tako.gen.ts location, then app/, then src/, then the project root. tako gen and tako g are aliases. When <app_root>/channels/ or <app_root>/workflows/ already exists, it also scaffolds empty definition dirs/files so they default-export defineChannel("<file-stem>") or defineWorkflow(...) stubs. Generated channel stubs use the file stem as the initial name, but tako generate does not rewrite existing explicit names. Generated TakoChannels entries use the declared name as the key and import("tako.sh").InferChannel<typeof import("./channels/<file>").default> for params, messages, and transport metadata. App code imports tako from tako.sh for project runtime state:

import { tako } from "tako.sh";

export default function fetch(request: Request) {
  tako.logger.info("request", { env: tako.env, build: tako.build });
  return new Response(
    `env=${tako.env} build=${tako.build} db=${tako.secrets.DATABASE_URL ? "ok" : "missing"}`,
  );
}

Surface

Export	Description
tako	Frozen runtime object with env, ports, paths, logger, secrets, and storages
tako.env	ENV value ("development", "production", ...)
tako.isDev	true when tako.env === "development"
tako.isProd	true when tako.env === "production"
tako.port	Port assigned to this app instance
tako.host	Host/address Tako bound this app instance to
tako.build	Build identifier (from TAKO_BUILD)
tako.dataDir	Persistent app-owned data directory — writes survive restarts
tako.appDir	Directory the app is running from (equivalent to process.cwd())
tako.secrets	Typed secret bag (interface regenerated from .tako/secrets.json)
tako.storages	Typed storage bag (interface regenerated from tako.toml)
tako.logger	Structured JSON logger (tako.logger.info(...))
Env	TypeScript union of configured environment names
TakoSecrets	TypeScript interface of secret names
TakoStorages	TypeScript interface of storage names
TakoRuntime	TypeScript type of the exported tako object

Secrets

tako.secrets is a Proxy that:

• Reads from a mutable store populated via fd 3 at startup (before user module is imported)
• Individual access works: tako.secrets.MY_KEY returns the string value
• Resists bulk serialization: toString(), toJSON() return "[REDACTED]"
• Is typed — the TakoSecrets interface augmentation in tako.d.ts lists every key present in .tako/secrets.json

The generated declaration file is type-only and is not imported by app code. In the browser, use tako.sh/client for channels, or tako.sh/react for channel hooks.

Images

JavaScript can create public optimized image URLs with imageUrl:

import { imageUrl } from "tako.sh";

const photo = imageUrl("/photos/p_123.jpg");
const url = imageUrl("/avatars/u_123.png", { width: 640 });
const avifUrl = imageUrl("https://cdn.example.com/uploads/avatars/u_123.png", {
  width: 640,
  format: "avif",
});

The helper returns /_tako/image?src=...&w=... and is synchronous. Width must be one of 320, 640, 960, 1200, 1920; quality is 1..100; format is webp or avif. Omit format for the optimizer default; Tako defaults to WebP, and format: "avif" is only valid when the app's [images].formats allows AVIF. Local public paths are available by default. Remote URLs must match [images].remote_patterns in tako.toml. Sources may be JPEG, PNG, GIF, WebP, or AVIF; animated GIF and WebP sources keep animation for optimized resize and crop URLs when emitted as WebP. AVIF output is available for still images; animated sources that request AVIF fall back to WebP. The server verifies the app's configured image guardrails before fetching or transforming.

Storage

Attach S3-compatible storage with the CLI, then use tako.storages.<name> from server-side app code:

tako storages add uploads \
  --provider s3 \
  --bucket app-uploads \
  --endpoint https://<account>.r2.cloudflarestorage.com \
  --region auto

import { tako } from "tako.sh";

const downloadUrl = await tako.storages.uploads.createDownloadUrl("receipts/r_123.png", {
  expiresInSeconds: 3600,
});

const uploadUrl = await tako.storages.uploads.createUploadUrl("avatars/u_123.png", {
  contentType: "image/png",
});

Storage URLs are private by default and signed with SigV4. createImageUrl(key, { public: true, width }) uses the storage public_base_url and the public image optimizer. Private storage image transforms are not implemented yet; use createDownloadUrl for private direct object URLs.

Vite Plugin

For SSR framework builds (TanStack Start, Nuxt, SolidStart, etc.):

// vite.config.ts
import { defineConfig } from "vite";
import { tako } from "tako.sh/vite";

export default defineConfig({
  plugins: [tako()],
});

On vite build: Emits <outDir>/tako-entry.mjs — a wrapper that normalizes the compiled server module into a default-exported fetch handler. Point main in tako.toml at this file.

On vite dev: Adds .test to allowed hosts. If PORT env var is set, binds Vite to 127.0.0.1:$PORT with strictPort: true (used by tako dev).

Next.js Adapter

For Next.js standalone builds:

// next.config.mjs
import { withTako } from "tako.sh/nextjs";

export default withTako({});

withTako() sets output = "standalone" and points adapterPath at the Tako adapter shipped in the SDK.

On next build, the adapter:

• copies public/ into .next/standalone/public/ when standalone output exists
• copies .next/static/ into .next/standalone/.next/static/ when standalone output exists
• writes .next/tako-entry.mjs

The generated wrapper prefers .next/standalone/server.js when it exists. Otherwise it falls back to next start.

Point your Tako deploy main at .next/tako-entry.mjs, or use the nextjs preset so that default is provided for you.

Enabling .enqueue() / signal() / channel publish inside Next.js routes

The Tako Next.js adapter spawns next start as a child process and proxies to it, so the Tako SDK boot hook that runs in the parent process never fires inside your Next.js routes. Add a Next.js instrumentation.ts at your project root to install the runtime once per server process:

// instrumentation.ts
export async function register() {
  if (process.env.NEXT_RUNTIME === "nodejs") {
    const { initServerRuntime } = await import("tako.sh/internal");
    initServerRuntime();
  }
}

After this, server-side routes and server actions can call defineWorkflow(...).enqueue(payload), signal(event, payload), and channel .publish(...) normally. Without it, those calls throw TakoError("TAKO_UNAVAILABLE", "Workflow runtime not installed. ...").

Types

import type { FetchHandler, TakoOptions, TakoStatus } from "tako.sh";

// FetchHandler = (request: Request, env: Record<string, string>) => Response | Promise<Response>

// TakoStatus — returned by the internal health endpoint
interface TakoStatus {
  status: "healthy" | "starting" | "draining" | "unhealthy";
  app: string;
  version: string;
  instance_id: string;
  pid: number;
  uptime_seconds: number;
}

Channels

Durable pub-sub routes with SSE and WebSocket transport, plus a bounded replay window. Channels are broadcast streams, not work queues: all authorized subscribers to the same channel read the same messages, and each subscriber keeps its own cursor. Production stores replay by deployed app id ({name}/{env}); local dev keeps replay in memory for the current daemon process.

Defining channels (file-based)

Drop one file per channel in <app_root>/channels/*.ts that default-exports defineChannel("<name>", ...).$messageTypes<M>(). The first argument is the wire channel name; generated files conventionally use the file stem, but discovery trusts the explicit name and rejects duplicate declared names. Server code imports the file directly to publish.

// <app_root>/channels/chat.ts
import { defineChannel } from "tako.sh";

interface ChatMessages {
  msg: { text: string; userId: string };
  typing: { userId: string };
}

export default defineChannel("chat", {
  paramsSchema: (t) => t.Object({ roomId: t.String({ minLength: 1 }) }),
  auth: {
    headerName: "authorization",
    async verify(input) {
      // input.params.roomId is typed; operation = "subscribe" | "publish" | "connect"
      const userId = await getUserId(input.header);
      if (!userId) return false;
      return { subject: userId };
    },
  },
  handler: {
    msg: async (data, ctx) => {
      await db.saveMessage(ctx.params.roomId, data);
      return data; // fanned out to subscribers
    },
    typing: async (data) => data,
  },
  replayWindowMs: 24 * 60 * 60 * 1000,
  inactivityTtlMs: 0,
  keepaliveIntervalMs: 25_000,
  maxConnectionLifetimeMs: 2 * 60 * 60 * 1000,
}).$messageTypes<ChatMessages>();

• The first argument is the channel name. defineChannel("chat") maps to /_tako/channels/chat; generated files conventionally use the file stem as the initial name.
• paramsSchema serializes to JSON Schema; tako-server validates query params before app auth.
• .$messageTypes<M>() is a type-level narrower that declares the message map — runtime no-op. Omit for channels with no typed messages.
• auth is optional. Omit or set false for public channels.
• handler presence decides transport: present → WebSocket, absent → SSE (broadcast-only). SSE channels reject client POST publishes.
• Every publish is stored before delivery. Messages are not claimed or removed when one subscriber receives them. replayWindowMs defaults to 10 minutes and can be overridden per channel.
• Browser clients reconnect until explicitly closed. Network loss, laptop sleep, server restarts, and clean connection rotation are transient; the SDK retries with bounded backoff, wakes early on the browser online event, and resumes from the last received message id while it remains inside the replay window.

Auth return values: false deny · true allow anonymously · { subject } allow with identity.

Publishing messages (server-side)

Import the channel module. The export is a typed handle (unparameterized) or a callable taking its params (parameterized). publish payloads are type-checked against the declared message map.

// Unparameterized channel: direct surface
import status from "../channels/status";
await status.publish({ type: "ping", data: { at: Date.now() } });

// Channel with params: bind params, then publish
import chat from "../channels/chat";
await chat({ roomId: "room1" }).publish({
  type: "msg",
  data: { text: "hello", userId },
});

Subscribing / connecting (client-side)

In the browser, use the Channel class from tako.sh/client with the declared channel name and optional params. subscribe() returns an EventSource-shaped subscription; connect() returns a WebSocket-shaped socket.

import { Channel } from "tako.sh/client";

// SSE channel — listen to the raw EventSource
const status = new Channel("status");
const token = await getToken();
const sub = status.subscribe({ authorization: token });
(sub.raw as EventSource).addEventListener("message", (e) => {
  const msg = JSON.parse(e.data) as { type: string; data: unknown };
  // ...
});
sub.close();

// WebSocket channel with params
const room = new Channel("chat", "ws", { roomId: "room1" });
const socket = room.connect({ authorization: token });
(socket.raw as WebSocket).addEventListener("message", (e) => {
  const msg = JSON.parse(e.data);
  // ...
});
socket.send({ type: "typing", data: { userId: "me" } });

// Publishing from the browser (WS channels only)
await room.publish({ type: "msg", data: { text: "hi", userId: "me" } });

authorization is optional. Omit it for public or cookie-auth channels; use headers.Authorization when the app expects a custom authorization value.

For React apps, prefer useChannel from tako.sh/react — it wraps Channel with buffered state, reconnects, and an onMessage callback.

React

tako.sh/react exposes a single useChannel hook. SSE is the default; pass transport: "ws" for WebSocket.

import { useChannel } from "tako.sh/react";

function ChatRoom({ room, token }: { room: string; token?: string }) {
  const { messages, status, error } = useChannel<{ body: string }>("chat", {
    params: { roomId: room },
    authorization: token,
  });
  if (error) return <p>error: {error.message}</p>;
  return (
    <ul>
      {messages.map((m) => (
        <li key={m.id}>{m.data.body}</li>
      ))}
    </ul>
  );
}

WebSocket with send:

const { messages, send } = useChannel("chat", {
  params: { roomId: room },
  transport: "ws",
});

Return shape (ChannelConnection<T>): messages (capped at 500, oldest-first), status ("connecting" | "open"), error, clear(), and send(data) on WebSocket only.

Reacting to messages imperatively

Pass an onMessage handler when you want to fire a side effect on each incoming message (toast, external store, ref update) without wiring a useEffect around the messages array. The hook uses a latest-ref internally, so the handler does not need to be memoized and swapping it does not reconnect:

useChannel("notifications", {
  onMessage: (msg) => toast(msg.data.text),
});

Sharing one connection across components

Each useChannel call opens its own SSE/WebSocket. When multiple components in the same tree need the same channel, call the hook once in a provider and fan out via context:

const BroadcastCtx = createContext<ChannelConnection<Msg> | null>(null);

export function BroadcastProvider({ children }: { children: React.ReactNode }) {
  const ch = useChannel<Msg>("demo-broadcast");
  return <BroadcastCtx.Provider value={ch}>{children}</BroadcastCtx.Provider>;
}

export function useBroadcast() {
  const ctx = useContext(BroadcastCtx);
  if (!ctx) throw new Error("useBroadcast outside BroadcastProvider");
  return ctx;
}

One connection, one buffer, any number of consumers.

Network routes

Direction	Method	Path	Transport
Subscribe	GET	/_tako/channels/<name>	SSE (text/event-stream)
Connect	GET	/_tako/channels/<name>	WebSocket (Upgrade: websocket)
Publish	WS	/_tako/channels/<name>	JSON text frame
Auth callback	POST	/channels/authorize	Internal (Host: <app>.tako)

Workflows

Durable background tasks with retries, schedules, and step checkpointing.

Authoring workflows

Drop a file in <app_root>/workflows/<name>.ts with a default export. The first arg is the workflow name (conventionally the kebab-case file basename), the second is a WorkflowOpts object with handler plus optional runtime settings:

// <app_root>/workflows/send-email.ts
import { defineWorkflow } from "tako.sh";

export default defineWorkflow<{ userId: string; to: string }>("send-email", {
  retries: 3, // retries after first attempt (default 2)
  schedule: "0 9 * * *", // cron: daily at 9am (5-field)
  worker: "email", // optional worker group; omitted means "default"
  concurrency: 10, // max parallel runs per worker (default 10)
  timeoutMs: 30_000, // handler timeout (default Infinity)
  backoff: { base: 1_000, max: 3_600_000 }, // exponential backoff
  handler: async (payload, ctx) => {
    ctx.logger.info("send-email started");
    const user = await ctx.run("fetch-user", (step) => {
      step.logger.info("fetching user");
      return db.users.find(payload.userId);
    });
    await ctx.run("send", (step) => {
      step.logger.info("sending email");
      return sendEmail(user, payload.to);
    });
  },
});

Enqueuing

Import the workflow module. The default export is a typed handle with .enqueue(payload, opts?) — payload is constrained to the declared P.

import sendEmail from "../workflows/send-email";

await sendEmail.enqueue({ userId: "u1", to: "a@b.c" });

await sendEmail.enqueue(payload, {
  runAt: new Date(Date.now() + 60_000), // delay
  retries: 9, // override workflow default
  uniqueKey: "digest:2026-04-14", // idempotency: no-op if non-terminal run exists
});

No generated file is needed for workflow enqueue typing — the types flow from the workflow module itself.

Workflow context (ctx)

The handler's second argument is the workflow context. Use ctx in examples.

Member	Description
ctx.run(name, fn, opts?)	Memoized step — replays stored result on retry instead of re-executing
ctx.sleep(name, durationMs)	Durable sleep — short sleeps inline, long sleeps (≥30s) defer the run
ctx.waitFor<T>(name, opts?)	Park until signal(name) arrives or timeout; returns T | null
ctx.bail(reason?)	End cleanly as cancelled (no retries)
ctx.fail(error)	End as dead immediately (no retries)
ctx.logger	Workflow-scoped logger
ctx.runId	The id of the current run
ctx.workflowName	The name of the current workflow
ctx.attempt	The current run attempt number (1-indexed; bumps on each run-level retry)

ctx.run options:

• retries?: number — in-step retry attempts (default 0)
• backoff?: { base?, max? } — in-step backoff
• retry: false — any throw inside fn immediately fails the run

The ctx.run(name, fn, opts?) callback receives a step context named step.

Member	Description
step.logger	Step-scoped logger (<workflow>:<step>)
step.stepName	The current step name
step.runId	The id of the current run
step.workflowName	The name of the current workflow
step.attempt	The current run attempt number (1-indexed)

ctx.waitFor options:

• timeout?: number — ms until the step resolves to null (default: park indefinitely)

Signals

// Wake all waitFor("approval:order-abc") calls with a payload
import { signal } from "tako.sh";
await signal("approval:order-abc", { approved: true });

Run lifecycle

pending → running → succeeded | cancelled | dead

• Throwing a regular error triggers the run-level retry path (exponential backoff).
• ctx.bail() → cancelled, no retries.
• ctx.fail() → dead, no retries.

tako.toml configuration

[workflows]                # base config inherited by every worker group
workers = 1                # 0 = scale-to-zero (default)
concurrency = 10

[workflows.email]          # named worker-group override
workers = 2

[servers.lax.workflows]    # base override on one server
concurrency = 20

[servers.lax.workflows.email]
workers = 4

• workers = 0 — scale-to-zero: worker starts when runnable work appears from enqueue, signal, cron, delayed retry/sleep, or lease reclaim, then exits after 300s idle.
• Precedence for worker: "email": [servers.<name>.workflows.email] > [servers.<name>.workflows] > [workflows.email] > [workflows] > defaults.
• If <app_root>/workflows/ exists but no workflow config exists, the app is implicitly scale-to-zero on every server.

Common Mistakes

1. CRITICAL: Using the Vite plugin for non-SSR apps

// WRONG — plain fetch handler app doesn't need the Vite plugin
// vite.config.ts with tako() plugin + src/index.ts with a fetch handler

// CORRECT — the Vite plugin is only for SSR framework builds
// For plain apps, just export a fetch handler and set main in tako.toml

2. HIGH: Forgetting the Next.js helper for standalone deploys

// WRONG — plain Next config without the Tako helper
export default {};

// CORRECT — let Tako configure standalone output and adapterPath
import { withTako } from "tako.sh/nextjs";

export default withTako({});

3. HIGH: Serializing the secrets object

import { tako } from "tako.sh";

// WRONG — bulk access is redacted
console.log(JSON.stringify(tako.secrets)); // "[REDACTED]"

// CORRECT — access individual secrets by name
const dbUrl = tako.secrets.DATABASE_URL;